1. Field of the Invention
This invention relates generally to semiconductor power switches and more particularly to a normally-off cascode power switch fabricated in wide bandgap semiconductor material, such as silicon carbide or gallium nitride.
2. Description of the Prior Art
Semiconductor power switches are generally well known in the art and comprise many types of circuit configurations, one of which is the cascode power switch. One such power switch is known to include a normally-on (depletion mode) conducting junction gated transistor (e.g., the junction field effect transistor (JFET), static induction transistor (SIT), or metal semiconductor field effect transistor (MESFET)) as the high-voltage device connected in cascode circuit relationship with a normally-off (enhancement mode) non-conducting metal oxide semiconductor field effect transistor (MOSFET) as the low-voltage device. The normally-off low voltage device is designed to block approximately 20V to 50V, thus providing sufficient reverse gate-source bias on the high voltage normally-on device to promote current pinch-off. An arrangement using a normally-off silicon MOSFET as a control device, however, cannot operate at relatively high operating temperatures, for example in the range of 125° C. which greatly restricts the design parameters in systems such as modern high power motor drivers, directed energy weapon systems and power supply switching and conversion systems.